1. Field of the Invention
The present invention relates to a backlight module for optical display and more particularly, to an optical film for backlight modules that can concentrate light rays and enhance the luminance.
2. Description of the Related Art
An optical film is a fine structure commonly used to enhance the luminous efficiency. However, when using an optical film, the mounting order and the orientation of the optical film must be carefully controlled. Improper installation causes the optical film unable to carry out the effect.
FIG. 1 is an exploded view of a backlight module using optical films such as brightness enhancement films (hereinafter referred as “BEFs”). As illustrated, the backlight module comprises a light guide plate 1, a diffuser 2, two BEFs 3 and 4. The light guide plate 1 fogs a linear light source into a uniform area light source. The diffuser 2 is covered on the top side of the light guide plate 1 to diffuse light rays evenly. The two BEFs 3 and 4 are arranged in proper order on the top side of the diffuser 2, each having parallel prisms 3a or 4a that condense light rays to enhance the luminous efficiency of the light guide plate 1 and to further enhance the luminance of the backlight module.
To ensure high performance of the two BEFs 3 and 4, the side of the first BEF 3 carrying the prisms 3a and the side of the second BEF 4 carrying the prisms 4a must face the same direction during installation, and the prism extending direction of the first BEF 3 must define with the prism extending direction of the second BEF 4 a contained angle. Preferably, the prism extending direction of the first BEF 3 and the prism extending direction of the second BEF 4 are arranged at right angles.
However, because the BEFs 3 and 4 are two separated members, they are arranged one above the other on the diffuser 2 in proper order. During the assembly process, the operator may attach the two BEFs 3 and 4 back to back erroneously or have the prism extending direction of the first BEF 3 and the prism extending direction of the second BEF 4 be arranged in parallel. When one of these mistakes occurred, the backlight module must be dismounted and reworked, thereby complicating the assembly process and increasing the work time.